docs: implement ChatAgent documentation and reasoning flow

[D3n3bX]

Description

This PR adds the technical documentation for the ChatAgent, the default specialized agent in the Perry ecosystem.

Key Technical Implementations

• Persona Enforcement: Documented the strict professional, formal, and humorless communication style required for Perry.
• Reasoning Transparency: Integrated the logic, allowing the Orchestrator to display Perry's internal process (, , , etc.).
• Robust JSON Parsing: Added documentation on the multi-layered parsing strategy (Regex + + ) used to handle inconsistent LLM outputs.
• Observability: Detailed the Logfire spans and instrumentation that provide full traceability for every chitchat interaction.

Agent Architecture

The serves as a blueprint for specialized agents, demonstrating:

1. Pydantic-AI initialization.
2. Async generator-based method.
3. Strict Pydantic validation for system-wide consistency.

This documentation aligns with the recently implemented README and architecture diagrams.